The evidence suggesting Attention-Deficit/Hyperactivity Disorder (ADHD) has neurodevelopmental roots with specific impairment in executive functioning continues to grow. However, no known study to date has explored the relationship between adult males with a diagnosis of ADHD and performance on a measure of executive functioning, the Delis-Kaplan Executive Function System (DKEFS). The current investigation attempted to explore (1) whether adult males with ADHD show an overall pattern of executive dysfunction as measured by the DKEFS, (2) potential group differences on both level-of-performance and process-oriented measure scores, and (3) the clinical utility of the DKEFS in diagnosing ADHD in adult males. A sample of 37 adults with ADHD was compared to a community sample of equal size. Multivariate statistical analysis yielded significant group differences despite intellectual advantage by the study group. In addition, analysis of individual measures revealed patterns which were not initially predicted based upon current theories of ADHD. Overall, however, no clinically significant impairments emerged, as defined by scores at least one standard deviation below the mean. These findings and potential clinical implications are discussed with recommendations for future research.